Degradation of poly[bis(glycine ethyl ester)phosphazene] in aqueous media

Abstract

The degradation of poly[bis(glycine ethyl ester)phosphazene] in aqueous media was studied by following the appearance of some of its expected by-products in solution. Disc-shaped polymer slabs of 12 mm diameter and 1.2 mm thickness were prepared by compression moulding, followed by incubation in aqueous media under carefully controlled conditions of pH and temperature. Low molecular weight by-products (phosphate and glycine) were assayed for up to 60 d using ultraviolet and visible spectroscopy. Slabs placed in pH 12.0 media at 20°C took 16 d to disappear completely (no longer visible), while at 37 and 47°C this occurred in 12 d. Also, slabs placed in pH 7.0 and 4.0 media took 60 and 24 d, respectively, to disappear at 47°C. However, at 20 and 37°C only some of the material disappeared at pH 7.0 after 60 d. In all cases, the cumulative fractional loss of by-products from the slabs was <1, indicating the presence in solution of other species which were unaccounted for. This study showed that poly[bis(glycine ethyl ester)phosphazene] slabs have a lifetime in physiological media which makes them an acceptable support for short-term controlled drug release, and complements others, in which polyphosphazenes were used for a similar application.